Radio frequency (RF) spectrum is a valuable commodity in today's world. There are more people desiring to use the RF spectrum than there is spectrum to go around, so use of the spectrum must be regulated. In many countries, the RF spectrum is regulated by governmental bodies. The Federal Communications Commission (FCC) regulates the RF spectrum in the United States.
The RF spectrum is regulated usually in one of two ways. A first way that governmental bodies regulate the RF spectrum is to sell portions of it to the highest bidder. The winning bidder then has exclusive use of the particular portion of the RF spectrum that he has just purchased. This is the way that RF spectrum for cellular telephones, television and radio channels are allocated. Single user allocations are the preferred method for applications where interference from other sources cannot be tolerated.
A second way that the government regulates RF spectrum usage is to create certain bands where anyone can use the RF spectrum as long as they comply with specified spectrum usage rules. For example, in the United States, the FCC has created three such bands. These bands are called the industrial, scientific, and medical (ISM) and the unified national information infrastructure (UNII) bands and are in the 900 MHz, 2.4 GHz, and 5.7 GHz portions of the RF spectrum. Anyone may use the spectrum in these bands as long as they are able to accept interference from other users and do not cause undue interference to other users.
The ISM and UNII bands have created a huge market for wireless consumer electronics products, such as cordless telephones, wireless computer products, and wireless computer networks. However, the popularity of the bands has resulted in a problem that many product developers did not anticipate, namely, performance degradation due to inter-product interference.
In wireless computer networks, the performance degradation is seen mainly in the network's data transfer rates. A wireless network today is capable of delivering a data transfer rate of 11 Mbps or more in an interference free environment, but if interference is introduced, the data transfer rate may drop to only a small fraction of the maximum.
Interference to a wireless computer network may come from many different forms. Sources of interference may include large appliances in the environment, other electronic devices such as pagers, cordless telephones, and microwave ovens, and other wireless computer networks. The relatively simple sources of interference such as appliances and pagers and telephones are relatively simple to deal with because their interference is periodic and is usually predictable. Because the interference is predictable, it is usually easy to avoid.
When multiple wireless computer networks are operating in the same general vicinity, the wireless networks can be interfere with one another. If the wireless computer networks are of the same type (the networks use a common technical standard), then there are often built-in mechanisms that permit the networks to remain operating at near optimal levels. However, if the wireless computers networks are of differing types, then there normally no built-in techniques that will permit the networks to work around each other.
Interference from wireless networks are more difficult to deal with due to the bursty nature of computer traffic and the fact the networks are often adaptive and can adjust their behavior depending on network conditions. The adaptive behavior often makes the interference worse because in many cases the network simply increases its transmission power when it detects a decrease in data rate. The increased transmission power results in a corresponding increase in the interference to other networks.
One proposed solution involves taking snapshots of the transmission spectrum and searching the snapshots to detect the presence of interference. When and if the interference can be detected and classified, the wireless communications network can alter its transmission behavior to circumnavigate the interference. However, due to the bursty nature network traffic, it is often the case that by the time an interferer has been detected, classified, and the network's behavior adjusted, the interferer has disappeared or moved to a different portion of the spectrum.
Another proposed solution involves the use of an arbitration unit (or a fixed priority scheme) to mediate between multiple wireless communications networks to reduce collisions between the transmissions of the various networks. In this solution, a prioritized list is used to allow transmissions of higher priority the ability to preempt transmissions of lower priority. Such a solution requires the use of additional hardware and software in order to coordinate the operation of the multiple wireless communications networks. Additionally, in the case of the fixed priority scheme, low-priority transmissions may be starved if the networks transmit too many high-priority transmissions.
A need has therefore arisen for a solution that allows multiple wireless communications networks operate within the same general vicinity without requiring collaboration between the wireless communications networks.